There are standard approaches for implementing model development tools. One approach is to have a specialized application, i.e., one application for one class of models. For example, a text editor can edit text. However, the text editor is limited to only editing text. Another approach is to have unified modelling frameworks, i.e., different classes of models are developed in the same environment with a limited set of specialized features. Both approaches are widely used by software providers. For example, there are many applications that allow a user to edit extensible markup language (XML) documents. Such applications do not have complete understanding of a nature and semantics of XML elements and their attributes inside the XML document. This requires from the user a complete low-level understanding of how a model is encoded into the XML format. Some other applications provide specialized plug-ins for editing a limited set of XML documents such as XML schemas, or extensible hypertext markup language (XHTML). The disadvantage of the existing frameworks is that they either do not provide enough specialized modelling features, or implementing specialization is similar to implementing a stand-alone application for a particular class of model, which is an expensive and time consuming process.